Carbon-based fossil fuels, such as coal, petroleum and natural gas, are finite and non-renewable resources. At the current consumption rate, supplies of fossil fuels will be exhausted in the near future. In addition, burning fossil fuels has resulted in a rise in the concentration of carbon dioxide in the atmosphere, which is believed to have caused global climate change.
Biofuels are viable alternatives to fossil fuels for several reasons. Biofuels are typically renewable energy sources produced from biomass, a material derived from recently living organisms. Because transportation-related gasoline consumption represents the majority of all liquid fossil fuel use, supplementing or replacing liquid fossil fuel (e.g. gasoline) with liquid biofuels can reduce our reliance on fossil fuels, and lower the amount of carbon dioxide released into the atmosphere.
The energy benefit of using biofuels such as ethanol (obtained from, for example, sugar cane, potato, manioc, and maize) has been questioned. Ethanol has a lower energy content than gasoline, therefore, more ethanol is required to provide the same energy output as gasoline. More significantly, the production of both ethanol and lipids (e.g. obtained from biodiesel) is currently driven by the use of fossil fuel. For example, the energy required for producing ethanol includes running farm machinery and irrigation, transporting and grinding the crop, producing pesticides and fertilizer, and fermenting and distilling ethanol. There have been concerns that the energy input for ethanol production may exceed the energy output from the combustion of ethanol. In addition, widespread production and use of ethanol and biodiesel will require constructing new distribution pipelines, because neither is suitable for transportation using existing fuel-distribution infrastructure. Moreover, any large-scale development of crop-based fuels such as ethanol and traditional biodiesel will compete for the same resources as food production (e.g. farm land and water), and ultimately be limited by the amount of arable land.
Currently, much work has been focused on refining algal oil using techniques used in the refining of vegetable oils. To date, however, none of these methods have worked for refining algal oil. Thus, a need exists for methods to refine algal oils.
Vegetable oils such as soy, canola, and camelina are essentially pure triglycerides of C16-18 free fatty acids which are extracted or expelled from the seeds of the plants where they are stored for energy. The resulting oil compositions can then be refined, bleached, and deodorized (RBD) to afford the final product oils as pure, crystal-clear materials that can be used in the food industry, soap industry, or biodiesel industry. These triglycerides are also the feedstock of choice for hydrotreating routes to jet fuel (UOP) and green diesel (UOP and Neste). However, due to the food versus oil debate, and the rising cost of vegetable oils the economic and social viability of these biofuels is questionable. A source of triglycerides is needed that does not compete with land used for commercial agriculture.
As mentioned above, vegetable oils such as soy, are purified by the RBD process in which trace levels (e.g. 1% or less) of phospholipids and free fatty acids are removed. Even lower levels of components such as sterol glucosides and chlorophyll are also removed. The small amounts of removed components can be treated as waste.
In theory, it is possible to purify algal oil using the RBD process described above. However, one fundamental difference between algal oil and traditional vegetable oils described above is that algal oil is harvested from the whole algal biomass and not selectively from a triglyceride storage system such as a seed. Algae oil is typically not essentially pure triglycerides, but rather a combination of triglycerides and significant levels (e.g. 1% to more than 40%) of a variety of other oil or lipid components, for example, chlorophylls and/or chlorophyllides, isoprenoids (including carotenoids), and phospholipids. For example, saline algae such as Duneliella viridis can deliver oils containing 30-40% of phospholipids. In addition, all photosynthetic algae deliver oils containing significant levels (for example, from about 0.6% to about 62% w/w) of chlorophyll or derivatives of chlorophyll.
The problem is that food-oil processing methods (such as RED) can deliver triglycerides ideally suited for converting to fuels, but a large fraction of the crude oil extracted (comprising, for example, phospholipids, chlorophyll, and free fatty acids) from algae (e.g. 10%-50%) is lost as waste making the overall economic and environmental aspects of using algae impractical. Thus, there is a need for a refining (“upgrading”) technology that removes, for example, undesirable heteroatoms (e.g. P, N and metals) from an oil composition without loosing potential sources of hydrocarbon fuels as waste.
Furthermore, at commercial scale, it is economically desirable to transport the refined (“upgraded”) algae oil by existing pipelines used by the petroleum industry. Additional sources of transport include, for example, truck, rail, and ship. Even if the heteroatoms (for example, P, N and metals) are removed from the oil composition the resulting “Green Crude”—like vegetable oils—will be excluded from transport via pipelines because of its high oxygen content, oxidative instability, and corrosivity, among other reasons.
Therefore, there is a need to remove essentially or almost essentially all heteroatoms (for example, O, P, N, and S) along with metals, and metalloids, if present, from an oil composition to deliver a refined oil composition comprising a hydrocarbon fraction that is essentially or almost essentially devoid of these components and that can be transported via existing pipelines, and/or further refined in existing refinery infrastructures.
In order to use the existing petroleum infrastructure, for example, refineries and pipelines, biofuel, such as an oil composition obtained from a biomass needs to be “upgraded”. Upgrading includes, for example, the removal of heteroatoms (S, N, O, P), removal of metals or metalloids, saturation of double bonds and/or aromatics by addition of hydrogen, isomerization of the carbon backbone to introduce branches to the backbone, and/or reforming to make aromatic compounds.
Provided herein are methods and systems useful for the upgrading of an oil composition.